The present invention relates to a rotation amount detecting system of a deflection mirror for an optical disc drive to read/write data from/to an optical disc.
Recently, technology in the field of magneto-optical disc drives has been greatly improved such that a data recording density on a magneto-optical disc has reached in excess of 10 Gbits/inch2.
In such an optical disc drive, an objective optical system is mounted on an arm which is movable in a transverse direction of tracks formed on an optical disc for rough tracking. Firstly, the rough tracking is performed to locate the optical head in the vicinity of the track. Then, the incident angle of a beam which is incident on the objective optical system is adjusted (i.e., a fine tracking is performed), with use of a galvano mirror or the like. During the fine tracking operation, the beam spot is accurately located on one of the tracks whose pitch is, for example, 0.34 xcexcm. In order to control the galvano mirror to accurately perform the fine tracking, it is necessary to detect the amount of rotation of the galvano mirror. In particular, it is desirable that the rotation amount of the galvano mirror can be detected without being affected by a tilting error of the galvano mirror.
Specifically, in a disc drive described above, if the galvano mirror is rotated to a position out of a certain rotational range to adjust the position of the beam spot, optical performance of the disc drive may be significantly lowered. Thus, the rotation angle of the deflection mirror should be monitored and controlled so as not to exceed a predetermined rotational range.
It is therefore an object of the invention to provide an improved rotation amount detecting system with which the rotation amount of the deflection mirror can be detected accurately without being affected by a tilting error of the deflection mirror.
For an object, according to the invention, there is provided a rotation amount detecting system for detecting a rotation amount of a deflection mirror rotatable about an rotation axis employed in an optical disc drive, which is provided with a light emitting system that emits a light beam to the deflection mirror, the light beam having a line-like cross section extending in a direction perpendicular to the rotation axis, and a detecting system that receives the beam reflected by the deflection mirror and determines the rotation amount of the deflection mirror in accordance with the received beam.
Since the light beam incident on the deflection mirror has a line-like cross section extending in the direction perpendicular to the rotation axis of the deflection mirror, the rotation amount can be detected without being affected by a tilting error of the deflection mirror.
Optionally, the light emitting system may include a light source that emits a diverging light beam, and a lens system provided between the light source and the deflection mirror, the lens system having a power at least in a direction parallel to the rotation axis of the deflection mirror.
Preferably, the lens system may convert the diverging light beam into a parallel beam in a direction perpendicular to the rotation axis of the deflection mirror.
In particular, the detecting system may have a photo detector having at least two light receiving areas arranged in a direction where the received beam is deflected if the deflection mirror rotated and a second lens system provided between the deflection mirror and the photo detector. In this case, preferably, the reflected beam passed through the second lens system forms a substantially circular spot on the two light receiving areas.
It is possible that the detecting system detects the rotation amount of the deflection mirror based on a difference between amounts of light received by the at least two light receiving areas.
In particular case, the light source may have a light emitting diode, and the lens system comprises an anamorphic lens.
Alternatively, the light emitting system may include a light source that emits a parallel light beam, and a lens system provided between the light source and the deflection mirror, the lens system having a power at least in a direction parallel to the rotation axis of the deflection mirror.
In this case, the lens system may have a power only in the direction parallel to the rotation axis of the deflection mirror.
In particular case, the light emitting system may have a beam splitter that splits the light beam emitted by the light source of the optical disc drive into a first beam to be directed to the optical disc and a second beam to be directed to the lens system.
When the light source emits the parallel beam, the lens system may have a cylindrical lens.
Also in this case, a photo detector may have at least two light receiving areas arranged in a direction where the received beam is deflected if the deflection mirror rotated, and a second lens system provided between the deflection mirror and the photo detector. The second lens system may a power only in a direction parallel to the rotation axis of the deflection mirror.
Further, the detecting system may detect the rotation amount of the deflection mirror based on a difference between amounts of light received by the at least two light receiving areas.
Further optionally, the detecting system may detect an intensity of the light beam emitted by the light source in accordance with a sum of the amounts of light detected by the two light receiving areas.